Exact match on column values A1&B1 with 2 other columns:

(bool) =MATCH(1, (A1=Column1) * (B1=Column2),0)

Arithmetic on a boolean results in a number. eg. TRUE * FALSE = 0.
Only TRUE * TRUE will result in the “1″ MATCH is looking for.

(list of values for validation combobox) =OFFSET(Start_point,MATCH(1, (A1=Column1) * (B1=Column2), 0),1,COUNTIF(column2,A1),1)